1. Field of the Invention
The subject invention relates to a valve spring retainer for operatively retaining a return spring on the stem of a poppet valve in an internal combustion engine.
2. Description of the Prior Art
The use of valve spring retainers in internal combustion engines is well known. Self locking retainers are known wherein the retainer automatically locks on the valve stem as the retainer is pressed onto the valve stem by reaction with the spring during operation. Such a retainer typically includes a retainer flange extending annularly about a hole on a central axis for engaging the top of a spring. A ring is disposed below the flange and extends about the axis for surrounding a valve stem. An inner portion extends cylindrically about the axis and axially between the ring and the flange. A skirt portion is spaced radially from and extends cylindrically about the inner portion and depends axially from a root diameter adjacent the flange to a distal end diameter. A plurality of slots extend radially from the hole and divide the flange and the portions into sectors leaving the ring to interconnect the sectors. During operation the spring reacts against a retainer flange and urges the sectors to rotate into engagement with the stem to lock onto the stem. The spring is centered by the skirt. Such assemblies are shown in U.S. Pat. No. 5,293,848 to Rich et al and applicant's previous U.S. Pat. No. 4,879,978; 5,143,351; 5,226,229; and 5,255,640.
The slots dividing the retainer into sectors must be narrow to prevent the sectors from rotating excessively relative to one another because the sectors must react against one another in the circumferential direction to force the hole into locking engagement with the valve stem. Yet, it is difficult to fabricate a retainer with narrow slots due to the complexities of molding.